Systems and methods for transmitter diversity expansion

ABSTRACT

Methods and systems for transmitter diversity expansion are provided. The methods and systems include steps and modules for applying a number of data streams (K) to a larger number of antennas (N). This is performed by applying each of the data streams to a single base antenna, such that K data streams are applied to K base antennas, and by shifting and combining the K data streams to produce N-K data streams to apply to N-K extension antennas.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application havingSer. No. 60/675,203, filed Apr. 26, 2005, which is entirely incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure is generally related to digital communicationsand, more particularly, is related to systems and methods for datatransmission.

BACKGROUND

Communication networks come in a variety of forms. Notable networksinclude wireline and wireless. Wireline networks include local areanetworks (LANs), digital subscriber line (DSL) networks, and cablenetworks, among others. Wireless networks include cellular telephonenetworks, classic land mobile radio networks and satellite transmissionnetworks, among others. These wireless networks are typicallycharacterized as wide area networks. More recently, wireless local areanetworks and wireless home networks have been proposed, and standards,such as Bluetooth and IEEE 802.11, have been introduced to govern thedevelopment of wireless equipment for such localized networks.

A wireless local area network (WLAN) typically uses infrared (IR) orradio frequency (RF) communications channels to communicate betweenportable or mobile computer terminals and stationary access points orbase stations. These access points are, in turn, connected by a wired orwireless communications channel to a network infrastructure whichconnects groups of access points together to form the LAN, including,optionally, one or more host computer systems.

Wireless protocols such as Bluetooth and IEEE 802.11 support the logicalinterconnections of such portable roaming terminals having a variety oftypes of communication capabilities to host computers. The logicalinterconnections are based upon an infrastructure in which at least someof the terminals are capable of communicating with at least two of theaccess points when located within a predetermined range, each terminalbeing normally associated, and in communication, with a single one ofthe access points. Based on the overall spatial layout, response time,and loading requirements of the network, different networking schemesand communication protocols have been designed so as to most efficientlyregulate the communications.

IEEE Standard 802.11 (“802.11”) is set out in “Wireless LAN MediumAccess Control (MAC) and Physical Layer (PHY) Specifications” and isavailable from the IEEE Standards Department, Piscataway, N.J. IEEE802.11 permits either IR or RF communications at 1 Mbps, 2 Mbps andhigher data rates, a medium access technique similar to carrier sensemultiple access/collision avoidance (CSMA/CA), a power-save mode forbattery-operated mobile stations, seamless roaming in a full cellularnetwork, high throughput operation, diverse antenna systems designed toeliminate “dead spots,” and an easy interface to existing networkinfrastructures.

The 802.11a standard defines data rates of 6, 12, 18, 24, 36 and 54 Mbpsin the 5 GHz band. Demand for higher data rates may result in the needfor devices that can communicate with each other at the higher rates,yet co-exist in the same WLAN environment or area without significantinterference or interruption from each other, regardless of whether thehigher data rate devices can communicate with the 802.11a devices. Itmay further be desired that high data rate devices be able tocommunicate with the 802.11a devices, such as at any of the standard802.11a rates.

One challenge in designing a wireless transmission system involvestransmit beamforming using an antenna array. Beamforming focuses signalstoward a receiver in such a way that they combine at the receiverresulting in a stronger signal. If signals are transmitted off multipleantennas and focused toward a designated receiver rather than beingtransmitted in an omni-directional fashion, the composite phase andamplitude of the transmission determines the effectiveness of thebeam-forming. The phase and amplitude relationship between the transmitantennas is adjusted to focus this energy at the intended receiver. Oneway to adjust a beam-forming transmitter is to incorporate additionalcircuitry on the radio. The circuitry is used to compute and share theconditions observed by the receiver. The transmitter then performs acomplex calculation to adjust the beamforming antenna array. However,this solution can be expensive.

Increasing the effective signal strength and/or receiver sensitivityenables more efficient communications. Increased signal strength mayenable service providers to more effectively use their equipment.Consumers may realize a cost savings as well.

SUMMARY

Embodiments of the present disclosure provide systems and methods fortransmitter diversity expansion.

Briefly described, in architecture, one embodiment of the system, amongothers, can be implemented with a bypass module configured to receive Kdata streams and to relay the K data streams to K antennas of a set of Nantennas; and a diversity expansion module configured to provide N-Kdata streams for application to a set of N-K antennas based on the Kdata streams.

Embodiments of the present disclosure can also be viewed as providingmethods for transmitter diversity expansion. In this regard, oneembodiment of such a method, among others, can be broadly summarized bythe following steps: receiving K data streams; providing each of the Kdata streams to K antennas of a set of N antennas for transmission;providing N-K data streams to N-K unused antennas of the set of Nantennas based on the K data streams for transmission; and transmittingthe N data streams on the N antennas.

Other systems, methods, features, and advantages of the presentdisclosure will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a block diagram of an open system interconnection (OSI)layered model for data transmission.

FIG. 2 is a block diagram of a prior art system for implementingtransmitter diversity.

FIG. 3 is a block diagram of an exemplary embodiment of a system fortransmitter diversity expansion according to the present disclosure.

FIG. 4 is a detailed block diagram of an exemplary embodiment of thecyclic shift module of the system for transmitter diversity expansion ofFIG. 3.

FIG. 5 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 3 with the cyclic shift modulebefore the combine module.

FIG. 6 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 3 with the combine module beforethe cyclic shift module.

FIG. 7 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 5 with two data stream inputsand four transmit antennas.

FIG. 8 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 7 with a Walsh combinationmatrix.

FIG. 9 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 5 with two data stream inputsand three transmit antennas.

FIG. 10 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 5 with three data stream inputsand four transmit antennas.

FIG. 11 is a block diagram of an exemplary embodiment of the system fortransmitter diversity expansion of FIG. 5 with two data stream inputsand six transmit antennas.

FIG. 12 is a flow diagram of an exemplary method embodiment of thesystem for transmitter diversity expansion of FIG. 5.

FIG. 13 is a flow diagram of an exemplary method embodiment of thesystem for transmitter diversity expansion of FIG. 6.

DETAILED DESCRIPTION

Disclosed herein are various embodiments of transmitter diversityexpansion systems and methods. Such embodiments provide for theapplication of a number of data streams (K) to a larger number ofantennas (N). One system embodiment comprises a module that applies eachof the data streams to a base antenna, such that K data streams areapplied to K base antennas. Also the system embodiment provides forshifting and combining of the K data streams to produce N-K data streamsfor application to N-K extension antennas. The described systems andmethods may be embodied in any type of processor such as a PHY layerprocessor, though not limited to a PHY layer processor, including, butnot limited to, a digital signal processor (DSP), a microprocessor(MCU), a general purpose processor, and an application specificintegrated circuit (ASIC), among others.

A new standard is being proposed, referred to as IEEE 802.11n (the“802.11n proposal”), which is a high data rate extension of the 802.11astandard at 5 GHz and 802.11g at 2.4 GHz. Both of these standards useorthogonal frequency division multiplexing (OFDM), which is a signalingscheme which uses multiple, parallel tones to carry information. Thesetones are commonly called subcarriers. It is noted that, at the presenttime, the 802.11n proposal is only a draft and is not yet a completelydefined standard. Other applicable standards include Bluetooth, xDSL,other sections of 802.11, etc. To increase the data rate, 802.11n isconsidering using multiple input, multiple output (MIMO) functionalitywhich uses multiple transmit and receive antennas.

IEEE 802.11 is directed to wireless LANs, and in particular specifiesthe MAC and the PHY layers. These layers are intended to correspondclosely to the two lowest layers of a system based on the ISO BasicReference Model of OSI, i.e., the data link layer and the physicallayer. FIG. 1 shows a diagrammatic representation of an open systemsinterconnection (OSI) layered model 100 developed by the InternationalOrganization for Standards (ISO) for describing the exchange ofinformation between layers in communication networks. The OSI layeredmodel 100 is particularly useful for separating the technologicalfunctions of each layer, and thereby facilitating the modification orupdate of a given layer without detrimentally impacting on the functionsof neighboring layers.

At a lower most layer, the OSI model 100 has a physical layer or PHYlayer 102 that is responsible for encoding and decoding data intosignals that are transmitted across a particular medium. Above the PHYlayer 102, a data link layer 104 is defined for providing reliabletransmission of data over a network while performing appropriateinterfacing with the PHY layer 102 and a network layer 106. The networklayer 106 is responsible for routing data between nodes in a network,and for initiating, maintaining and terminating a communication linkbetween users connected to the nodes. A transport layer 108 isresponsible for performing data transfers within a particular level ofservice quality. A session layer 110 is generally concerned withcontrolling when users are able to transmit and receive data. Apresentation layer 112 is responsible for translating, converting,compressing and decompressing data being transmitted across a medium.Finally, an application layer 114 provides users with suitableinterfaces for accessing and connecting to a network. This OSI model 100can be useful for transmissions between, for example, two stations.

Exemplary embodiments of the diversity expansion techniques for atransceiver can be processed in a PHY signal processor. A PHY signalprocessor is configured to perform functionality of the preferredembodiments. A digital communication system may comprise such aprocessor, alone, or in combination with other logic or components. Asystem of communications may further be embodied in a wireless radio, orother communication device. Such a communication device may include manywireless communication devices, including computers (desktop, portable,laptop, etc.), consumer electronic devices (e.g., multi-media players),compatible telecommunication devices, personal digital assistants(PDAs), or any other type of network devices, such as printers, faxmachines, scanners, hubs, switches, routers, set-top boxes, televisionswith communication capability, etc. A Medium Access Control (MAC)Protocol enables the exchange of channel information between stations. Atransmitter may shift and combine data streams to achieve higherfidelity from the transmitter, thereby increasing the sensitivity of thereceiver.

Exemplary embodiments of transmitter diversity expansion systems andmethods described herein may be implemented in systems employing IEEE802.11 protocols. IEEE 802.11 modes may be implemented to use multipletransmit and receive antennas. When multiple transmit antennas are used,various purposes may be served. One purpose may include sending moredata through more antennas, or increasing the data capacity of atransmission. Data streams that are sent through a transmit channel maybe called “spatial streams.”

Another purpose for exploiting multiple transmit antennas is to send onedata stream through multiple paths. For instance, one stream can be sentmultiple times through multiple antennas to increase the strength of thereceive signal at another station. Multiple copies of the data streammay be sent on multiple antennas to increase the reliability of thecommunication. To exploit two antennas in a transmitter, two separatedata streams can be sent substantially simultaneously. This method isreferred to as “spatial multiplexing.” Alternatively, one spatial streammay be sent twice on the two antennas. One way of sending one spatialstream twice is space-time block coding (STBC) which may improve thereliability of the data link. A disadvantage of STBC is that thereceiver has to know that the transmitter is using this technique. Thatis, the receiver has to know how to use this technique to recover thedata. STBC is not seamless to the receiver. A goal for use of multipleantennas (e.g., two, three, four, etc.) is to send multiple data streamssuch that the receiver requires no special method to recover the data.

One way of accomplishing this latter goal is through beamforming, whichmay require extra communication overhead. An exemplary embodiment oftransmitter diversity expansion systems and methods uses a technique inwhich an extra transmit antenna may be utilized without the receiverneeding special decoding circuitry. Moreover, a receiver does not needto know whether or how this technique is applied at the transmitter. Onemechanism to accomplish transmit diversity expansion is through the useof cyclic shifts. The amount of cyclic shifts that is used in theimplementation is not important. That is, any appropriate cyclic shiftamounts may be used. One system for performing the cyclic shifts isprovided in FIG. 2.

Referring to FIG. 2, a combining module 210 and a shifting module 230 isshown. A module as used herein, may be embodied in software, hardware,firmware, etc., or a combination of these embodiments. The combiningmodule receives K spatial streams 200, where K is an integer value,greater than 1. The combining module 210 includes a unitary matrix or anextension matrix, which is applied to the K spatial streams. The matrixmay be a fast Fourier transform matrix. This matrix may be a rectangularmatrix, such that the output comprises N columns or rows 220 of datastreams, where N is an integer value, greater than or equal to K. SinceN is greater than or equal to K, K spatial streams 200 are mapped to Nantennas 250. After the combining at combining module 210, a cyclicshift is applied to each of the N data streams at shifting module 230.The cyclic shift allows for the combination of the K spatial streamswhile enabling a discernment of the individual streams. The cyclic shiftis applied to each of the N spatial streams independently. So, for acase of four spatial streams, in an exemplary embodiment, no cyclicshift is applied to the first stream of the four streams; a first cyclicshift is applied to the second stream of the four streams; a secondcyclic shift is applied to the third of the four streams; and a thirdcyclic shift is applied to the fourth of the four streams. For example,if a two by two unitary matrix is applied to one spatial stream, theyare added together, resulting in a one by two matrix.

Referring to FIG. 3, K spatial streams 300 are first passed to K basetransmit antennas 310 out of a total of N transmit antennas 310, 330.The N antennas, 310, 330 comprise K base antennas 310 and K-N extensionantennas 330. Then, the cyclic shift and unitary matrix are applied tothe K spatial streams in module 320. Module 320 comprises functionalityof modules 210 and 230 of FIG. 2. This result is applied to N-Kextension antennas 330 of the N antennas 310, 330. So, K spatial streams300 are applied to K base antennas 310 and N-K streams that have had acyclic shift and unitary matrix applied to them are applied to N-Kextension antennas 330. This is referred to herein as a “systematicmapping.” This technique (systematic mapping) may be applied in thepreamble portion of a packet. One advantage of such a method is that Kstreams 300 appear on K base antennas 310, which enables simple testingand verification. Because K transmit antennas can be connected directlyto K receive antennas, the spatial streams 300 are decoded without theextension antennas 330. Then, when the extension antennas 330 are added,a verification may be performed to verify that the same results arereceived with the N antennas 310, 330 as were received with the K baseantennas 310.

One non-limiting embodiment for applying a cyclic shift is shown in FIG.4. Modules 420, 440, and 460 are embodied in cyclic shifting andcombining module 320 of FIG. 3. The K data streams 400 are passedstraight through to K base antennas 410. In module 420, a cyclic shiftof −100 nanoseconds is applied to a spatial stream of K data streams400. The output of module 420 is sent to stage 430, which may be acombination stage or an antenna, among other stages. At module 440, a+100 nanosecond cyclic shift is applied to a spatial stream of K datastreams 400 and the output is sent to stage 450, which may be acombination stage or an antenna, among other stages. In module 460, a+200 nanosecond cyclic shift is applied to a spatial stream of K datastreams 400 and the output is sent to stage 470, which may be acombination stage or an antenna, among other stages. In an exemplaryembodiment, each of the cyclic shifted streams may be passed to asingular antenna of N-K antennas.

Referring to FIG. 5, transmit diversity expansion system 500 includingbypass module 510, cyclic shift module 530, and combining module 540 forexpanding K data streams to N antennas is shown. K streams 505 are sentto bypass module 510 and sent unchanged to K base antennas 520 . . . 520n. Bypass module 510 may simply be electrical conduits to pass K streams505 to K base antennas 520 . . . 520 n. In cyclic shift module 530, acyclic shift is applied to K streams 505 to provide K cyclic shiftedstreams 535. The K cyclic shifted streams 535 are then combined incombining module 540 to provide N-K streams 545. The N-K streams 545 areapplied to N-K extension antennas 550 . . . 550 n. So, spatial streams505 pass through bypass module 510 and are applied to base antennas 520. . . 520 n. The spatial streams 505 are also sent to cyclic shiftmodule 530, where various cyclic shift values are applied to each ofspatial streams 505. In the case of two spatial streams, one may beshifted and one may not be. Alternatively, one can be shifted a positiveamount and one shifted a negative amount, or one can be shifted a firstamount and one can be shifted a second, different amount. The differentamounts may be random or programmed. The shifted signals 535 arecombined using a matrix, such that N-K extension streams 545 that areshifted and combined are sent to N-K extension antennas 550 . . . 550n.

In one embodiment, the expansion process comprises two steps, namelycyclic shifts and combining. Both steps are linear operations that canbe represented with matrix multiplication, which may comprise twomatrices: one for cyclic shifts and one for combining. The system ofFIG. 5 may be represented as follows:W _(ext) =W _(combine) *W _(cs)where W_(combine) is a matrix, which defines the combining operation andW_(cs) is a matrix, which defines the cyclic shifts. W_(cs) is adiagonal matrix in which the diagonal elements are related to cyclicshift operations applied to the corresponding stream and allnon-diagonal elements are zeros.

An exemplary combining matrix may be defined as follows

$W_{combine} = {\left( {1/\left. \sqrt{}{Nss} \right.} \right)*\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}}$The W_(combine) matrix has a Walsh-Hadamard construct. The matrix istrimmed as needed. N-K rows are retained for N-K extension antennas. Kcolumns are retained for the K spatial streams. The matrixleft-multiplies the column vector of the base signals. The vector of thebase signals is loaded in the order of the K streams, with the firststream as the first (top) element in the column vector. The matrixoutput vector is sent to the cyclic shift module (e.g., such as module530). Power normalization may be achieved by using a scaling constant(Nss in the equation above), such that the extension antennas (N-Kantennas) are power-consistent with the base antennas (K antennas).

An exemplary cyclic shift matrix may be defined as follows:

$W_{cs} = \begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}$This matrix is a diagonal matrix of cyclic shift operators. The cyclicshift matrix is trimmed as needed to N-K by N-K, where N-K is the numberof extension antennas. An exemplary method embodiment for extending twodata streams to two extension antennas for a total of four antennas isrepresented as follows:

$\begin{bmatrix}{{Extend}\; 1} \\{{Extend}\; 2}\end{bmatrix} = {{\begin{bmatrix}{{CS}\; 1} & 0 \\0 & {{CS}\; 2}\end{bmatrix}\begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}}\begin{bmatrix}{{Base}\; 1} \\{{Base}\; 2}\end{bmatrix}}$

An alternative transmitter diversity expansion system 600 for performingthe cyclic shift and combine functions is provided in FIG. 6. Again, Kspatial streams 605 are sent through bypass module 610 to K baseantennas 620 . . . 620 n. K spatial streams 605 are also combined inmodule 635 by applying a unitary matrix to produce N-K streams 640. Acyclic shift is then applied to N-K streams 640 in cyclic shift module645 to produce N-K cyclic shifted streams 650, which are applied to N-Kextension antennas 655 . . . 655n. As a non-limiting example of twospatial streams, two spatial streams 605 are sent through bypass module610 to two base antennas 620, 620n and the two spatial streams 605 arecombined in module 635 by applying a unitary matrix to produce twocombined streams 640. Those two combined streams 640 are sent to cyclicshift module 645 where they are shifted to produce two (N-K) shiftedstreams 650 that are applied to two (N-K) base antennas 655, 655n.

In an alternative embodiment, the combining module precedes the cyclicshift module as shown in FIG. 6. This embodiment also represents alinear operation, which can be represented with a matrix multiplicationcontaining the two aforementioned matrices of cyclic shifts andcombining in reversed order as follows:W _(ext) =W _(cs) *W _(combine)where the W_(combine) matrix defines the combining operation and theW_(cs) matrix defines the cyclic shifts. In this case, the vector of theK base signals is loaded in the order of the K streams. This vector ofbase signals is left-multiplied with the combining matrix to form N-Kextension streams. The N-K extension streams are left-multiplied withthe cyclic shift matrix W_(cs). Again, the combining matrix W_(combine)may be based on Walsh-Hadamard construct and trimmed as needed. N-K rowsare retained for N-K extension antennas. K columns are retained for theK spatial streams. An exemplary embodiment for extending two datastreams to two extension antennas for a total of four antennas isrepresented as follows:

$\begin{bmatrix}{{Extend}\; 1} \\{{Extend}\; 2}\end{bmatrix} = {{\begin{bmatrix}{{CS}\; 1} & 0 \\0 & {{CS}\; 2}\end{bmatrix}\begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}}\begin{bmatrix}{{Base}\; 1} \\{{Base}\; 2}\end{bmatrix}}$

FIG. 7 provides another exemplary embodiment of a transmitter diversityexpansion system 700 with two spatial stream inputs 701, 710 and fourantennas 730, 740, 770, 780. Both streams 701, 710 pass through bypassmodule 720 and are applied unchanged to base antennas 730, 740respectively. Streams 701, 710 are also applied to cyclic shift module750. Stream 701 is shifted by cyclic shift submodule 755 and stream 710is shifted by cyclic shift submodule 760, both within cyclic shiftmodule 750. Cyclic shift submodule 755 shifts stream 701 by more or lessthan cyclic shift submodule 760 shifts stream 710, but not by the sameamount. Stream 702 is the shifted version of stream 701. Stream 712 isthe shifted version of stream 710. Streams 702, 712 are provided tocombining module 765 in which a unitary or extension matrix is appliedto the streams to produce streams 703 and 713. Streams 703 and 713 areapplied to extension antennas 775 and 780. In this exemplary embodiment,streams 701, 710, 703, 713 are transmitted from respective antennas 730,740, 775, 780 substantially simultaneously.

FIG. 8 is a similar exemplary embodiment of a transmitter diversityexpansion system 800 in which a Walsh matrix is used to perform thecombining module. Both streams 801, 805 pass through bypass module 810and are applied unchanged to base antennas 815, 820 respectively.Streams 801, 805 are also applied to cyclic shift module 825. Stream 801is shifted by cyclic shift submodule 830 and stream 805 is shifted bycyclic shift submodule 835, both within cyclic shift module 825. Cyclicshift submodule 830 shifts stream 801 by more or less than cyclic shiftsubmodule 835 shifts stream 805, but not by the same amount. Stream 802is the shifted version of stream 801. Similarly, stream 807 is theshifted version of stream 805. Streams 802, 807 are provided tocombining module 840 in which a Walsh-Hadamard combining matrix isapplied to the streams to produce streams 803 and 808. Streams 803 and808 are applied to extension antennas 845 and 850. In this exemplaryembodiment, streams 801, 805, 803, 808 are transmitted from respectiveantennas 815, 820, 845, 850 substantially simultaneously.

Referring now to FIG. 9, an exemplary embodiment of a transmitterdiversity expansion system 900 is provided for two spatial stream inputswith three antennas. Both streams 901, 905 pass through bypass module910 and are applied unchanged to base antennas 920, 930 respectively.Streams 901, 905 are also applied to cyclic shift module 940. Stream 901is shifted by cyclic shift submodule 945 and stream 905 is shifted bycyclic shift submodule 950, both within cyclic shift module 940. Cyclicshift submodule 945 shifts stream 901 by more or less than cyclic shiftsubmodule 950 shifts stream 905, but not by the same amount. Stream 902is the shifted version of stream 901. Stream 907 is the shifted versionof stream 905. Streams 902, 907 are provided to combining module 960 toproduce streams 903 and 908. If two extension antennas were being used,streams 903 and 908 would be applied to extension antennas 970 and 980.However, since only one extension antenna 970 is used in thisembodiment, only stream 903 is provided to extension antenna 970. Stream908 is pruned or discarded. In this exemplary embodiment, streams 901,905, 903 are transmitted from respective antennas 920, 930, 970substantially simultaneously.

Referring now to FIG. 10, an exemplary embodiment of a transmitterdiversity expansion system 1000 is provided for three spatial streaminputs with four antennas. Streams 1001, 1005, 1010 pass through bypassmodule 1015 and are applied unchanged to base antennas 1020, 1030, 1040respectively. Streams 1001, 1005, 1010 are also applied to cyclic shiftmodule 1050. Stream 1001 is shifted by cyclic shift submodule 1055,stream 1005 is shifted by cyclic shift submodule 1060, and stream 1010is shifted by cyclic shift submodule 1065, all within cyclic shiftmodule 1050. Each cyclic shift submodule 1055, 1060, 1065 shifts streams1001, 1005, 1010 by more or less than the other two cyclic shiftsubmodules. Stream 1002 is the shifted version of stream 1001. Stream1007 is the shifted version of stream 1005. Stream 1012 is the shiftedversion of stream 1010. Streams 1002, 1007, 1012 are provided tocombining module 1070 to produce streams 1017. If three extensionantennas were being used, three streams would be applied to theextension antennas. However, since only one extension antenna 1080 isused in this embodiment, only stream 1017 is applied to extensionantenna 1080. The other streams are pruned or discarded. In thisexemplary embodiment, streams 1001, 1005, 1010, 1017 are transmittedfrom respective antennas 1020, 1030, 1040, 1080 substantiallysimultaneously.

Referring now to FIG. 11, an exemplary embodiment of a transmitterdiversity expansion system 1100 is provided for two spatial streaminputs with six antennas—two base antennas and four extension antennas.Streams 1101, 1105 pass through bypass module 1110 and are appliedunchanged to base antennas 1115, 1120 respectively. Streams 1101, 1105are also applied to cyclic shift module 1125. Stream 1101 is shifted byboth cyclic shift submodule 1130 and cyclic shift submodule 1140. Stream1105 is shifted by both cyclic shift submodule 1135 and cyclic shiftsubmodule 1145. Cyclic shift submodules 1130, 1135, 1140, 1145 arelocated within cyclic shift module 1125. Each cyclic shift submodule1130, 1135, 1140, 1145 shifts streams 1101, 1105 by more or less thanthe other three cyclic shift submodules. Streams 1102, 1107 are shiftedversions of stream 1101. Streams 1104, 1108 are shifted versions ofstream 1105. Streams 1102, 1104, 1107, 1108 are provided to combiningmodule 1150 to produce streams 1112, 1114, 1117, 1118. In this exemplaryembodiment, streams 1101, 1105, 1112,1114, 1117, 1118 are transmittedfrom respective antennas 1115, 1120, 1160, 1170, 1180, 1190substantially simultaneously. The functionality of each module describedhereinabove may be distributed among one or more modules. Likewise, theentire functionality described hereinabove may be combined within asingle module for some embodiments.

A flow diagram of an embodiment of a transmitter diversity expansionmethod 1200 is provided in FIG. 12. This flow diagram is based on theexemplary embodiment with the cyclic shift module first, followed by thecombining module as provided in FIG. 5. In block 1202, K spatial streamsare selected for transmission on a set of N antennas, where N is greaterthan K. In block 1210, the K spatial streams pass through a bypassmodule. In block 1220 the K spatial streams are applied to K baseantennas. In block 1230, a cyclic shift is applied to the K data streamsto produce K shifted spatial streams. In block 1240, the K shiftedspatial streams are combined to produce N-K spatial streams. In block1250, the N-K spatial streams are applied to N-K extension antennas. Inblock 1260, the combined K unchanged spatial streams and N-Kshifted/combined spatial streams are transmitted on N antennascomprising K base antennas and N-K extension antennas.

Another flow diagram of an embodiment of a transmitter diversityexpansion method 1300 is provided in FIG. 13. This flow diagram is basedon the exemplary embodiment with the combining operation first, followedby cyclic shift operation as provided in FIG. 6. In block 1302, Kspatial streams are selected for transmission on a set of N antennas,where N is greater than K. In block 1310, the K spatial streams passthrough a bypass module. In block 1320 the K spatial streams are appliedto K base antennas. In block 1330, K data streams are combined toproduce N-K extension streams. In block 1340, a cyclic shift is appliedto the N-K extension streams. In block 1350, the N-K extension streamsare applied to N-K extension antennas. In block 1360, the combined Kunchanged spatial streams and N-K shifted/combined spatial streams aretransmitted on N antennas comprising K base antennas and N-K extensionantennas.

In summation, extra transmit antennas are exploited using a systematicmapping method of expanding spatial input streams such that a receiverdoes not need to be aware of any special coding.

Exemplary embodiments of the present disclosure can be implemented inhardware, software, firmware, or a combination thereof. In the preferredembodiment(s), transmitter diversity expansion systems and methods areimplemented in software or firmware that is stored in a memory and thatis executed by a suitable instruction execution system. If implementedin hardware, as in an alternative embodiment, the systems and methods ofthe preferred embodiments can be implemented with any or a combinationof the following technologies, which are all well known in the art: adiscrete logic circuit(s) having logic gates for implementing logicfunctions upon data signals, an application specific integrated circuit(ASIC) having appropriate combinational logic gates, a programmable gatearray(s) (PGA), a field programmable gate array (FPGA), etc.

The flow diagrams of FIGS. 12 and 13 show the architecture,functionality, and operation of possible implementations of thetransmitter diversity expansion software implementing transmitterdiversity expansion methods. In this regard, each block represents amodule, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that in some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in FIGS. 12 and 13. For example, two blocks shown insuccession in FIG. 12 may in fact be executed substantially concurrentlyor the blocks may sometimes be executed in the reverse order, dependingupon the functionality involved, as would be understood by thosereasonably skilled in the art of the present disclosure.

The transmitter diversity expansion program, which may comprise anordered listing of executable instructions for implementing logicalfunctions, can be embodied in any computer-readable medium for use by orin connection with an instruction execution system, apparatus, ordevice, such as a computer-based system, processor-containing system, orother system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, ordevice. More specific examples (a non-exhaustive list) of thecomputer-readable medium would include the following: a portablecomputer diskette (magnetic), a random access memory (RAM) (electronic),a read-only memory (ROM) (electronic), an erasable programmableread-only memory (EPROM or Flash memory) (electronic), and a portablecompact disc read-only memory (CDROM) (optical). In addition, the scopeof the present disclosure includes embodying the functionality of thepreferred embodiments of the present disclosure in logic embodied inhardware or software-configured mediums.

It should be emphasized that the above-described embodiments of thepresent disclosure, particularly, any “preferred” embodiments, aremerely possible examples of implementations, set forth for a clearunderstanding of the principles of the disclosure. Many variations andmodifications may be made to the above-described embodiment(s) of thedisclosure without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andprotected by the following claims.

1. A method comprising: receiving a first set of data streams;generating a second set of one or more data streams based on acombination of the first set of data streams, wherein the combination ofthe first set of data streams is the product of a matrix multiplicationof the data in the first set of data streams with a unitary matrix; andtransmitting each data stream of the first and second sets of datastreams from a separate antenna.
 2. The method of claim 1, wherein thesecond set of data streams comprises at least one data streamcorresponding to a cyclically-shifted combination of the data streams ofthe first set of data streams.
 3. The method of claim 1, wherein atleast one data stream of the first set of data streams iscyclically-shifted before it is combined with the other data streams ofthe first set of data streams to generate the second set of datastreams.
 4. The method of claim 1, wherein generating the second set ofdata streams based on a combination of the first set of data streamscomprises: combining the first set of data streams into a combined datastream; and cyclically-shifting the combined data stream to generate atleast one data stream of the second set of data streams.
 5. The methodof claim 1, wherein generating the second set of data streams based on acombination of the first set of data streams comprises:cyclically-shifting at least one data stream of the first set of datastreams; and combining the at least one cyclically-shifted data streamwith at least one other data stream of the first set of data streams. 6.The method of claim 1, wherein the unitary matrix is one of a FourierTransform matrix or a Walsh matrix.
 7. A system comprising: a signalprocessor configured to receive a first set of data streams, andgenerate a second set of one or more data streams based on a combinationof the first set of data streams, wherein the combination of the firstset of data streams is the product of a matrix multiplication of thedata in the first set of data streams with a unitary matrix; and aplurality of antennas, wherein each antenna is configured to transmit acorresponding one data stream of the first and second sets of datastreams.
 8. The system of claim 7, wherein the second set of datastreams comprises at least one data stream corresponding to acyclically-shifted combination of the data streams of the first set ofdata streams.
 9. The system of claim 7, wherein at least one data streamof the first set of data streams is cyclically-shifted before it iscombined with the other data streams of the first set of data streams togenerate the second set of data streams.
 10. The system of claim 7,wherein generating the second set of data streams based on a combinationof the first set of data streams comprises: combining the first set ofdata streams into a combined data stream; and cyclically-shifting thecombined data stream to generate at least one data stream of the secondset of data streams.
 11. The system of claim 7, wherein generating thesecond set of data streams based on a combination of the first set ofdata streams comprises: cyclically-shifting at least one data stream ofthe first set of data streams; and combining the at least onecyclically-shifted data stream with at least one other data stream ofthe first set of data streams.
 12. The system of claim 7, wherein theunitary matrix is one of a Fourier Transform matrix or a Walsh matrix.13. A computer-readable medium having instructions stored thereon that,if executed by a device, cause the device to perform a methodcomprising: receiving a first set of data streams; and generating asecond set of one or more data streams based on a combination of thefirst set of data streams, wherein the combination of the first set ofdata streams is the product of a matrix multiplication of the data inthe first set of data streams with a unitary matrix; transmitting eachdata stream of the first and second sets of data streams from a separateantenna.
 14. The computer-readable medium of claim 13, wherein thesecond set of data streams comprises at least one data streamcorresponding to a cyclically-shifted combination of the data streams ofthe first set of data streams.
 15. The computer-readable medium of claim13, wherein at least one data stream of the first set of data streams iscyclically-shifted before it is combined with the other data streams ofthe first set of data streams to generate the second set of datastreams.
 16. The computer-readable medium of claim 13, whereingenerating the second set of data streams based on a combination of thefirst set of data streams comprises: combining the first set of datastreams into a combined data stream; and cyclically-shifting thecombined data stream to generate at least one data stream of the secondset of data streams.
 17. The computer-readable medium of claim 13,wherein generating the second set of data streams based on a combinationof the first set of data streams comprises: cyclically-shifting at leastone data stream of the first set of data streams; and combining the atleast one cyclically-shifted data stream with at least one other datastream of the first set of data streams.
 18. The computer-readablemedium of claim 13, wherein the unitary matrix is one of a FourierTransform matrix or a Walsh matrix.